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Allergic reactions caused by poison ivy


When skin comes into contact with poison ivy sap, a painful allergic reaction called “contact dermatitis” or “Rhus dermatitis” may occur.

The substance that causes this allergic reaction is urushiol, a compound in the poison ivy sap. The sap is found in all parts of the plant except the pollen.

About 9 in 10 people are sensitive to poison ivy sap. They react to even minute quantities of urushiol. 


The symptoms of an allergic reaction to poison ivy usually appear 24 to 48 hours after contact with the sap.

The first sign of an allergic reaction to poison ivy is a strong itching with redness at the site of contact.

Afterwards, lesions may appear:

  • Inflammation
  • Swelling
  • Blistering
  • Crusting when blisters burst and leak

The seriousness of an allergic reaction depends on:

  • The person’s degree of sensitivity
  • The amount of sap that comes into contact with the skin
  • The area of the body affected

The most serious allergic reactions affect areas of the body where the skin is thin, like the face and the genitals.

Symptoms may be more severe in people who have had a significant allergic reaction to poison ivy in the past.

In most cases, symptoms last 7 to 10 days. When reactions are more severe, it can take up to 3 weeks to heal.

When to consult

See a doctor immediately if you have inhaled smoke from burning poison ivy plants. Inhaling such smoke can lead to extremely painful inflammation of the lungs and serious respiratory problems that can result in death.

See a doctor if you have swallowed poison ivy sap. The sap can damage the following organs:

  • Digestive tract
  • Respiratory tract
  • Kidneys

Also see a doctor if:

  • You have a severe rash.
  • You have a rash on several areas of your body.
  • You have a rash on sensitive areas of your body, such as your face, eyes or genitals.
  • Your symptoms last more than 3 weeks.
  • You have symptoms of infection in the affected areas despite treatment. Symptoms of infection include:
    • Increase in pain
    • Oozing pus
    • Redness
    • Increase in swelling 72 hours after contact with the sap


If your skin has come into contact with sap:

  • Wash exposed areas with cold water as soon as possible. Use a mild soap.
  • Make sure you remove all bits of the plant that could have been stuck under your nails.
  • Avoid rubbing your skin too hard.

To relieve your symptoms:

  • Apply cold compresses to the affected area for 15 to 30 minutes several times a day.
  • Take a warm bath with baking soda and colloidal oatmeal. Check with your pharmacist.
  • Avoid hot baths and showers. Hot water can increase redness, itching and swelling.

If poison ivy sap has gotten into your eyes, rinse them for 15 minutes under a gentle stream of warm tap water. Be sure to run the tap water directly on your eye, from the inner corner (near the nose) towards the outer corner.

See a healthcare professional if these measures are not enough to relieve your symptoms.

Note that antihistamines (drugs used to treat allergies) do not directly affect allergic reactions to poison ivy. These drugs aim to reduce or eliminate the effects of histamine, but the poison ivy does not cause the release of this substance.


The main complications that can occur include:

  • Infection in areas of the affected skin.
  • Damage to the lining of the lungs caused by the inhalation of smoke from burning poison ivy plants. These injuries can lead to serious respiratory problems that can result in death.


Poison ivy sap can easily stick to gardening tools, clothing and animal fur.

The urushiol in the sap, which is responsible for allergic reactions, is an oily substance that does not evaporate. It can therefore remain poisonous for several months. Be sure to take precautions when handling contaminated articles or dead or dry poison ivy plants.

Protection and prevention

You may come into contact with poison ivy during outdoor activities – during hikes in the woods, for instance. During such activities:

  • Always stick to the trails
  • Wear protective clothing, such as:
    • Long pants
    • Long-sleeved shirts
    • Closed shoes

For further information on how to identify, handle and get rid of poison ivy, read Identifying and getting rid of poison ivy.

Risk factors

Contact with poison ivy sap often occurs during outdoor activities.

Animals, dogs in particular, can directly contaminate people who touch them because the sap sticks to their fur.

Last update: June 13, 2023


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